In mammalian species, the organ in the uterus containing blood vessels that unites the fetus and mother, providing the fetus with oxygen and nutrients from maternal circulation while also removing waste products. Made by trophoblastic tissue and extra embryonic mesoderm.
See Amnion (or amniotic sac), Chorion, Dizygotic twins, Mesoderm, Monozygotic twins, Nicotine, Ontogenetic adaptation, Pulsatility index (PI)